Pt425d: modification 425 to Kubota 25hp diesel

[agjones]

I've not been shy about my dissatisfaction with the original loud, hot, thirsty robin eh72. And that was before it blew with less than 350 well maintained hours....and subaru failed to stand behind the warranty.

I replaced that unsupported gas guzzler with a thrifty Kubota d662 as an experiment. Verdict : Quieter, cooler, less of a drinking problem. I knew it'd be a little underpowered, plus losing 600 rpm results in reduced hyd flow and there is a hp hit just based on the engine power. It performs admirably. If I reduce the psi to 2000psi it would be a great match.

So with a stand-in machine buying some time, I'm pulling the d662 and replacing it with a d1105 at 25hp & 3000 rpm. Plenty of power. A little less flow. 6.8gpm to the pto by my math, unless you convinced me they used some kind of priority flow in Tazewell....

The new engine, rebuilt and shiny, needs 2" added to the tub rear wall to accommodate radiator and debris screen (lessons learned) no problem, I'd liberated it installing the d662... And the reconfigured engine cover is going to have removable side panels(instead of hinges) as well as bracing to support a rear 3pt lift from redland hill.

The oil cooler is moving, the fuel tank too... And I suspect we will wind up with a braced and shielded vertical exhaust.

If you have made it this far with me, yes I'm posting pics.

QUESTION : if I'm losing flow to the pto from reduced rpm, About a 15%hit, could I increase the relief setting to gain some hyd power? I get the difference between flow and pressure... But if I take fewer bites, can I take bigger ones is my question...

 

[MossRoad]

I'd think if you increase the relief pressure setting you stand a better chance of blowing a seal in something down the road. GPM doesn't care about pressure. Once a motor or cylinder hits an immovable force, pressure rises rapidly and looks for a relief, be it a relief valve or seal.

 

[Gravy]

Less flow will probably only matter for mowing. Most everything else done with a small PT is more dependent on pressure. I would never have imagined that a liquid-cooled 25hp diesel Kubota engine and cooling system could possibly fit in a PT425 tub with only 2 inches of extension. I will be watching closely to see how it works out.If you make it work, I may come to be in a lot of trouble with my wife...

 

[agjones]

The smaller diesel worked well enough to warrant doing it right...and needed the same space...it definitely worked hard mowing....

I've got other things to mow with...but I could also do some math and change the pulley size or motor on the finish mower I guess.

The brush cutter more brute... The power should be fine even at lower speed.

Less flow will probably only matter for mowing. Most everything else done with a small PT is more dependent on pressure. I would never have imagined that a liquid-cooled 25hp diesel Kubota engine and cooling system could possibly fit in a PT425 tub with only 2 inches of extension. I will be watching closely to see how it works out.If you make it work, I may come to be in a lot of trouble with my wife...

 

[MossRoad]

Are you driving the pumps directly from the motor or through pulleys?

 

[agjones]

The pulley of the finish mower deck is driven by a hydraulic motor at a rate determined by the flow through the pto...the hydraulic pumps are all mounted on the engine.

 

[ponytug]

Dear AGJones,

Let me just say that I'm impressed all around. 1st that you are running a word of mouth business on this, and second your confidence in tearing things apart to make them better.

(GPM * pressure)/1714 = HP, so yes, you are taking a 15% hit on delivered HP.

For 99% of my mowing, I'm not at max HP, so I'm not sure that it would make a difference to you either, unless you are mowing thick, wet grass most of the time.

Before getting too wound up about it, I would think about put a pressure gauge on the PTO while you mow, and see how often it hits max psi. If it isn't very often, you probably won't notice it. You might want to bear in mind that the extra torque on the diesel will make the engine more resistant to bogging down compared to the gasoline engine.

Just a small question on the photo- are you going to strengthen those engine mounts? It looks like they are flexed a bit under load.

All the best,

Peter

 

[agjones]

Peter

Thanks for the encouragement and input.

I'll take your advice on the gauge, good call. Sharp blades, raise the deck a notch, dry grass... I think I'll be good.


The mounts will get anti-vibration disks and a cross-brace X as we put the rear back together.

4 years with this machine, which I refer to as my exoskeleton, and I know exactly what I need from it. Being relatively uncomplicated, the PT is a great platform for modifications. As long as I stay focused on maintaining its inherent balance of think I'll be pleased with the changes....without overcomplicating it.

 

[agjones]

The PT 425d is alive. And is now a pt425dr.

My pt425 with 25hp robin subaru made it 325h and blew. What blew more? Robin subaru failed to honor the warranty.

After installing a Kubota d662 as a trial. Success but a little bit underpowered... The 2013 power trac 425 now sports a 24.7 hp Kubota d1105 coupled by bellhousing to tram+tandem hydraulic pumps.

Also added, redland hill 3pt hitch to the rear (the right in 425dr) with lift /float and down pressure. Controlled by a 2 spool valve on the steering column. Second spool is dedicated front grapple function, which leaves the qa on a dedicated lever. The front grapple function is useful in the 4n1, Minihoe, utility grapple, and a forthcoming rotating qa plate based on a helac rotary actuator.

Engine cover is now fixed (bolt to remove) with lift out sides. Diesel tank, air filter, exhaust moved to the top. A brush guard will be added to protect the tank and rops re installed a bit higher for my height (6'4 +hard hat! ) and suspension seat.

Switching the engine cover to aluminum, the heavier Kubota engine, hitch/hardware and 1/3 loaded rear tires (beet juice) reduce the effective center of gravity while maintaining the infamous pt-pucker positive lift weight indicator...

The radiator faces the rear of the machine, protected by the hitch frame and the expanded metal sides are being backed by smaller hole, swappable intake screens to reduce the clogging, dust at intake and cooling fins.

Pictures and updates are coming, enjoy this quick video for now.

Power trac 425 Kubota diesel d1105 - YouTube

 

[cqaigy2]

Wow, very nice! It will be nice to see how you set up your brush guards.